In communication networks, such as packet-switched networks, data traffic may be classified differently according to required or ordered service. A known mechanism for classification is quality of service (QoS).
In the internet, the most widespread IP-based QoS mechanism is based on the architecture for Differentiated Services described in “An Architecture for Differentiated Services” by S. Blake et al, RFC 2475 published by the Internet Engineering Task Force (IETF). In this architecture, data traffic is classified into different classes, where each class receives a different treatment at the nodes in the network. To which class a particular packet belongs is indicated by a DSCP-field in the IP-header of the packet, for example. Intermediate nodes in the network hence read the DSCP-field and deduce which treatment the packet gets.
Further, “Assured Forwarding PHB Group” by J. Heinanen, RFC 2597 also published by the IETF describes a class of traffic treatments called Assured Forwarding (AF). Here, nodes implementing the AF treatment have to allocate a configurable, minimum amount of forwarding resources, such as buffer space and bandwidth, to each implemented AF class and each class should be serviced in a manner to achieve the configured service rate, such as bandwidth, over both small and large time scales. In detail, three parameters may be defined, such as priority indicating the priority of the data traffic, minimum rate indicating the minimum rate that should be given to this class of data traffic and maximum rate indicating the maximum rate that should be given to this class of data traffic.
Typically, the minimum rates of all classes are serviced first in descending priority order. If there is bandwidth left after this, data traffic may be serviced in descending priority order up to the maximum rate for each AF class.
In such conventional fixed networks the bit rate of the outgoing link is constant, i.e., does not vary over time.
Another QoS framework has been discussed in 3GPP to provide QoS in Long Term Evolution (LTE) systems. For example, the 3GPP specification TS 23.401 “General Packet Radio Service (GPRS) Enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Access”, Version 8.1.0, March 2008, describes bearer-level parameters, such as QoS class identifier (QCI), that are signalled to the LTE radio access network (RAN) from a core network. According to this specification, a QCI is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment, e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc. and that have been pre-configured by the operator owning the access node, e.g. eNodeB.
3GPP has standardized the characteristics that the LTE RAN should provide for 9 of possible 256 QCIs, referred to as standardized QCIs, which may be found in the above mentioned 3GPP specification TS 23.401 describing the Evolved Packet System (EPS). Characteristics specified are Resource Type, Priority, Packet Delay Budget (PDB) and Packet Loss Rate (PLR), wherein values of the characteristics for the QCIs are given in the 3GPP specification TS 23.401, which is incorporated by reference.
In this QoS framework, the Priority levels shall be used to differentiate between service data flow (SDF) aggregates of the same user equipment (UE), and it shall also be used to differentiate between SDF aggregates from different UEs. Via its QCI an SDF aggregate is associated with a Priority level and a PDB. In the 3GPP specification, scheduling between different SDF aggregates shall primarily be based on the PDB. If the target set by the PDB can no longer be met for one or more SDF aggregates across all UEs that have sufficient radio channel quality then priority shall be used as follows: A scheduler shall meet the PDB of SDF aggregates on Priority level N in preference to meeting the PDB of SDF aggregates on Priority level N+1.
In the following, it should be noted that there is a notion about an absolute priority of Priority level N over N+1 when the PDB deadline is approached.
The 3GPP specification TS 23.401 differentiates between Guaranteed Bit-Rate (GBR) QCIs and non-GBR QCIs, wherein bearers associated with a GBR QCI have an additional parameter called GBR signalled to the RAN at the time of bearer setup. For such bearers, the RAN has the possibility to perform admission control based on the value of the GBR field. For bearers associated with a non-GBR QCI, no GBR value is signalled to the RAN at the time of bearer setup.
LTE systems will offer operators a high system capacity both in terms of throughput and number of users that can be supported simultaneously. These capabilities give operators the opportunity to offer a wide range of services and operators are expected to use the QoS mechanisms defined in 3GPP to differentiate the service quality and characteristics between their offered services.
However, with the conventional QoS framework presented above, traffic related to a QCI associated with a high priority, i.e. low Priority value, may starve out traffic from lower priority traffic. In other words, since the higher priority traffic is serviced by the scheduler with absolute priority, all resources or capacity will be given to that traffic at high load situations and there will be nothing left for lower priority traffic.
Therefore, strict priority scheduling with greedy traffic can cause starvation of lower priority traffic at high system loads.
In particular, in view of the specifics of wireless links, e.g. the time varying nature of the bandwidth of wireless links, simply applying the above described aspects for fixed networks is not sufficient, since starvation of lower priority traffic may not be avoided, especially when served traffic decreases and overhead increases in a mobile environment with users with bad radio conditions.